The key is the large hose connections on both sides of the box. The
original fresh only side air boxes have round connections for the large
hose on each side and these connect very near the front of the van. The
later boxes with side heat use oval connections for the large hose on
each side and these connect to the box area farthest from the front of
the van.

The original set of side connections is in front of the heater core,
fresh only. The other set is behind the heater core, so when the core is
warmed the side vent air is warmed.

Many later boxes have both position connections available but the pair
not used are sealed up. To switch from one connection point to the other
means different hoses, at least in the case of wanting to use the oval
heated air ports. These heated ports are in tight areas of the dash that
require special molded elbows to adapt from the oval box ports to the
round vent hoses.

The switch from fresh only to heated side vents occurred during the 1987
production year. Early 87 uses the old hose connection points while
later 87 made the switch.

Mark

Frank Condelli wrote:
>          Does anyone know how to tell the difference between the front heater boxes that have heat output to the side vents in the dash and the ones that do not ?  What can I see from the outside of the box that would tell the difference ?
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> Cheers,
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